Vulcanization of rubber



a sure of 4 mm., the

Patented Jan. 2, 1945 UNITED STATES. PATENT orrics VULCANIZA'IION F RUBBER Arnold R. Davis, Riverside, Com, assimor to American Cyanamid Company, N. Y.,' a corporation oi Maine New Yorln.

No Dra. Application August so, 1941, Serial N 409.000

19 Claims. (Cl. 260-782) This invention relates to the vulcanization of rubber and more particularly to the control of the activity of accelerators which possess a tendmay to scorch the rubber at processing temperatures, e."g., those occurring in the milling, calendering, extruding, etc. operations or even in 'st rasa- It is known add acids to rubber for the purpose of preventing or minim ng scorchin or premature vulcanization of the rubberdue to the activity oi vulcanization accelerators at the lower or processing temperatures.

l have discovered a new class or acid retarders The monoterpene maleic anhydride addition products .or adducts may be distilled under low to obtain a distillate which has been described as the volatile dibasic acid anhydride or the addition product. For example, at a prestion' containing the volatile dibasic acid.anhydrid e of the monomeric terpene was distilled over in the temperature range oi 160-178" C. The non-volatile residue from the distillation will contain anhydrides of terpene polymers according to the work or E. R. Littman reported in Ind. and Eng. Chem., 28, 1986, pages In the practice or the invention the acid retarder i incorporatedlnto the unvulcanized rubher. preferably prior to orat about the. time or the addition of the accelerator to the rubber.

The ret'arder may be the complete-monoterpencmaleic anhydride addition product. the volatile dibasic acid anhydride. the non-volatile residue,

or the acids obtainable from these anhydrides y hydrolysis. In its preferred form the invention contemplates the use or the complete monoterpene-maleic anhydride addition product '(acid anhydride).

The novel retarders of my invention being resinous and non-crystalline acids will more. easily disperse in the rubber than crystalline acid retarders such as benzoic and salicylic acid.

. Elustrative of the accelerators with which my acid retarders may be employed for the purpose of preventing or reducing scorching of the rubber are the sulfur-containing accelerators such as mercaptobenzothiaacle, benzothlazyl disulfide, the aldehyde-amine accelerators such as butyl and heptyl aldehyde-aniline, and the cliaryl l0 guanidine accelerators such as diphenyl and (11-0- tolyl guanidine. They may also be used for retarding the activity of accelerator combinations of the character wherein a basic material is used to activate the primary accelerator such as combinations of an acidic type sulphur-containing accelerator and a diaryl guanidine, for example, mcrcaptobenzothiazole and dlphenyl guanidine or di-ortho-tolyl guanidine.

The invention is illustrated by the following 2.0 specific examples to which however, it is not intended that the invention be limited. The parts are by weight.

Example 1 thiazyl de activated with diphenyl guanidine was employed asthe accelerator. Samples were prepared. cont 1.; a monoterpenemaleic anhydride addition product (adduct) and the volatile dibasic anhydride and the non-volao tile residueoi an addition product, respectively,

' and in addition a control containing no acid retarder. The samples were made up in the following proportions: D

samples were then tested in a ,Williams photometer using a 8 minute "11 value at 100 C.

The results were as follows;

' a B -o 1) No he... -4--. .0s0 .052 .011;

Aiter Lshoursinweierst as o 101 .084 .078 chanson-am" t.. +2 +2.44 0 +7 1 Alter ii hours In water at 05C.. .170 .120 .110 .151 Ghana-.. ..percont.. +1001 +46. 8 +52. 5

The lower percent change in the Williams u value aiter heating indicates the rubber to have. scorched lees From the above results it is apparent that the benzothiazyl disulfldwdiphenyl zuanidine accelerator retarded with the acid materials gives less premature vulcanization than this accelerator combination alone.

The samples were then tested atiullcure and showed theiollowlniz pool properties:

soccer? the activity of e accelerator or, acceltor com bination employed, and, in general, the proportions willbe about il.1% toohout 1% on the weight of the rubber.

e the invention has been more particularly described with reference to the use of the acids as accelerator retarders in the vulcanmetion of oat rubbers, they may he used in like capacity in the rulcation oi synthetic rubhere such HModulus (at 530%) and tensile in lbsJsq. in.

9 Elongation at-broek in percent.

The above results show that while the acidic materiels'reterci'the action of the accelerator. at 85 (1. one ct processing temoeratureo, they have little or no effect on the accelerator action at the uulction temperature,

comuoun the rubber mixes, the resinous acid retarcierc may teuol to stick to the it but this may be easily overcome by adding to smell amount cl oteoric acioi to the rubber, either as such, or in combination with the acid rel-order cc a fusion product obble by melting to= gcther the two materials. I

Example 2' Mcrcaptothiazoie was employed as the accelerator cool as c rctarder therefor, therewao used rccocctively. to complete monoterpene malcic we 1r uncle audition product and a complete addition product combineii with c acides'an unti-tacii'lu the .ioi'm oi u tuslon product. The temples were compounded in the folio prooortionc: I a x Com- These samples were then given set-up tests in a William plastometer employing a 3 minute "11" value at 100 C. 3

No host AiierLfihonrsinwaieratBPC Change +1. 1 +1. 1 AltaruhonrsinwsteratBB'C- not .097 Change.-. +5. 5 +7. 76

The tests show that the monoterpene-maleic anhydride addition products have a very decided 1 retarding eflect on the activity of mercaptobenzothiazole'both when used alone'and in combina.- tion with stearic acid.

As will be understood .art, the proportions of the acids incorporated into the rubber may bevaried with the oi retarding action desired 01' with by-those skilled inthe cc hutociiene-ucrylonitrile and hutodlene-styrene copolymers. Therefore, in the claims, the term rubber is intended to include-the srntheticrubhero oi the character described, cc well as the ueiturcl rubbers.

This opplication is' o continuotion-in-pert oi my tic-pending application, Serlel No. stucco, filed Jon. c, 1940.

Since verietions and w may he mode in the invention without departing from the spirit or scope thereof, the foregoing description is not intended by way of limitation of the invention except as may he defined in the appended claims. What E claim is:

i. In the vulcanization of rubber with e vul- "Mk ogent and on acceieretor which is suiflcitly ective to cause premature vulcanization oi? the rubber, the improvement which comprises controlling the activity oil the accelerator by in- .corooraung in the rubber o small amount of c resinous material selected from the group consistinu oi monotei'pcioc-moleic divide addition product, aclrldes thereof anol the acids ohtoiueol by hytlr sic oi said'drldes.

2. in the Anita-$1011 of rubber with a vulmm m i. and an accelerator which is outflclently active to cause premature vulconizction oi the rulclzer, the improvement which comprises,

controlling the activity oi the accelerator by incorporatlno in the rubber a small amount of o. resinous moncterpene maleic anhydride addition product. v I

e. in the vulcanization of rubber with a vul- 1.1, agentnnd an organic suliur-con accelerator which is sumciently active to cause premature vulcanization of the rubber, the improvement whichv comprises controllins the cctivlty of the accelerator by incorporating in the rubber a small amount of aresinous material selected from the group consisting of monoter- .oene-moleic anhydride addition product, drides thereof and the acids obtained by hydrolysls of said anhydrides.

4. In the vulcanization oi. rubber with a vulg agent and an organic cultur-coutoiuing accelerator which is sumciently active to cause premature vulcanization of "the rubber. the improvement which comprises controlling. the ootivity of theaccelerator by incorporating in the rubber a small am unt oi a r monoterpene maleic anhydri e addition product.

5. In the vulcanization of rubber with a vulagent, and an accelerator combination of an anionic ammo-containing aseasrv a diaryl guanidine activator therefor, which accelerator combination is sumclently active to cause premature vulcanization of the rubber, the improvement which comprises controlling the activity of the accelerator combination by incorporating in the rubber a small amount or a resinous material selected from the group consisting of monoterpene-maleic anhydride addition product, anhydrides thereof and the acids obtained by hydrolysis of said anhydrides.

6. In the vulcanization of rubber with a vulcanizing agent and an accelerator combination of an organic sulfur-containing accelerator and a diaryl guanidine activator therefor, which accelerator combination is sumciently active to cause premature vulcanization or the rubber, the improvement which comprises controlling the activity of the accelerator combination by incorporating in the rubber a small quantity of a resinous monoterpene-inaleic anhydride addition product.

7. The process of claim 5, in which the diary] guanidine activator is diphenyl guanidine.

8. The process of claim 5, in which the diaryl guanidine activator is di-o-tolyl guanidine.

9. In the vulcanization of rubber with a vulcanizing agent and diphenyl guanidine as the accelerator, the improvement which comprises controlling the activity of the diphenyl guanidine by incorporating in the rubber a small quantity of a resinous monoterpene-maleic anhydride addition product.

10. Unvulcanized rubber containing a vulcanizing agent, an accelerator which is sufficiently active to cause premature vulcanization of said rubber, and a small quantity of a resinous material selected from the group consisting of monoterpene -maleic anhydride addition product, anhydrides thereof and the acids obtained by hytive to cause premature vulcanization of said rubber, and a small quantity of a resinous monoterpene-maleic anhydride addition product.

'tion product.

12. Unvulcanized rubber containing a vulcanizing agent, an organic sulfur-containing accelerator which is sumciently active to cause premature vulcanization of said rubber, and a small amount of a resinous material selected from the group consisting of monoterpene-maleic anhydride addition product, anhydrides thereof and the acids obtained by hydrolysisof said anhydrides.

13. Unvulcanized rubbercontaining a vulcanizing agent, an organic sulfur-containing accel-' erator which is sufliciently active to cause premature vulcanizationof said rubber, and a small amount of a resinous monoterpene-maleic anhydride addition product.

14. Unvulcanized rubber as in claim 13, in which the organic sulfur-containing accelerator is mercaptobenzothiazole.

15. Unvulcanized rubber containing a vulcanizing agent, an organic sulfur-containing accelerator, a diaryl guanidine activator therefor, and a small quantity of a resinous material selected from the group consisting of monoterpene-maleic anhydride a'ddition product, anhydrides thereof and the acids obtained by hydrolysis of said anhydrides.

16. Unvulcanized rubber containing a vulcanizing agent, an organic sulfur-containing accelerator, a diaryl guanidine activator therefor, and a" small quantity of a resinous monoterpenemaleic anhydride addition product.

17. Unvulcanized rubber containing a vulcanizing agent, benzothiazyl disulfide, a diaryl guanidine activator therefor, and a small amount of a resinous monoterpene-maleic anhydride addi- 18. Unvulcanized rubber as inclaim 17, in which the diaryl guanidine activator is. di-orthotolyl guanidine.

19. Unvulcanized rubber containing a vulcanizing agent, diphenyl guanidine as the accelerator, and a small amount of a resinous monoterpenemaleic anhydride addition product.

ARNOLD'R. DAVIS. 

